Ballast-free tank



FIG. 1 is a perspective view of a ballast-free tank comprising the new design;

FIG. 2 is a front side view thereof, where the right side, the left side, and the rear side views are mirror images thereof;

FIG. 3 is a top view thereof; and,

FIG. 4 is a bottom view thereof.

The broken lines depict portions of the ballast-free tank that form no part of the claimed design. 

CLAIM The ornamental design for a ballast-free tank, as shown and described. 